Horticulture Principles and Practices

Germination Test In

Germination Test In laboratory practice (according to the AOSA Rules for Testing Seed), seed germination is defined as “the emergence from the seed embryo of those essential structures which, for the kind in question, are indicative of the ability to produce a normal plant under favorable conditions.” It is important to note that a germination test is not designed to predict how seed will perform in the field. Favorable conditions are used so the test can be easily reproduced between labs (Figure 9). Vigor testing (tests that subject the seed to types of stress) are designed to mimic field conditions and are a better indicator of field performance. 400 seeds are always planted in a standard germination test. The seed is taken from the pure seed component of the purity test. Depending on seed size, four to sixteen replicates may be used. Seed is either counted and planted by hand or a vacuum planter is used (Figure 10). Many different types of substrate are used for germination tests. Blotters, towels, and filter paper are the most common, but creped cellulose paper and sand are also widely used (Figure 11). Water is the commonly used as the moisture, but in dormant species potassium nitrate (KNO 3 ) is also used. FIGURE 9 Typical germination workroom with growth chambers and workbench. (Source: Annette Miller, USDA-ARS National Center for Genetic Resources Preservation. Fort Collins, Colorado). FIGURE 10 A vacuum planter aids in planting by selecting a set number of seeds in a uniform pattern. (Source: Annette Miller, USDA-ARS National Center for Genetic Resources Preservation. Fort Collins, Colorado). FIGURE 11 Germination Rolled Towels Small. Safflower planted in special seed germination towels. (Source: Annette Miller, USDA-ARS National Center for Genetic Resources Preservation. Fort Collins, Colorado). 9.4 Seed Quality Analysis 291

Once planted, the seed is placed into a growth chamber. Chambers are set at various temperatures, and some even alternate temperature between night and day to simulate natural conditions (Figure 12). Crops that were developed closer the equator usually have a single temperature, such as wheat (20 degrees C). Native species in north America usually require alternating temperatures, such as blue grama (20C at night, 30C during the day). As soon as the seeds develop discernable structures they can be evaluated. Just because a seed sprouts does not mean it is counted as viable. All the structures must be present and in working order for the seed to be considered normal (Figures 13 and 14). When evaluating, the analyst separates the seed into five categories: normal, abnormal, dead, hard, and dormant (a TZ test is used to determine dormancy). Only normal, hard, and dormant seeds are counted as viable. Tetrazolium Testing (TZ) A TZ test is a quick way to determine total viability. The test usually takes 24 hours to complete, and is the primary method for determining dormancy. The steps FIGURE 12 Typical growth chamber. (Source: Annette Miller, USDA-ARS National Center for Genetic Resources Preservation. Fort Collins, Colorado). FIGURE 13 Triticale is grown on towels. This sample is ready to be evaluated. (Source: Annette Miller, USDA-ARS National Center for Genetic Resources Preservation. Fort Collins, Colorado). FIGURE 14 The three beans on the left have sprouted, but are missing primary leaves—thus they are considered abnormal. (Source: Annette Miller, USDA-ARS National Center for Genetic Resources Preservation. Fort Collins, Colorado). 292 Chapter 9 Sexual Propagation